


Invariance

by picturestoproveit



Series: Missing Scenes [2]
Category: Agents of S.H.I.E.L.D. (TV)
Genre: Canon Compliant, Cunnilingus, Dirty Talk, Episode: s03e18 The Singularity, F/M, Missing Scene, One Shot, POV Leo Fitz, Praise Kink, Vaginal Sex, Zero Chill To Be Found, so tons of swearing
Language: English
Status: Completed
Published: 2021-02-07
Updated: 2021-02-07
Packaged: 2021-03-17 04:06:50
Rating: Explicit
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 6,594
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/29219202
Author URL: https://archiveofourown.org/users/picturestoproveit/pseuds/picturestoproveit
Summary: Twenty-four hours ago, Fitz had been happily cuddled up with the woman of his dreams and  perfectly content with his place in the universe.So naturally, the universe decided to drop the ceiling on his head.
Relationships: Leo Fitz/Jemma Simmons
Series: Missing Scenes [2]
Series URL: https://archiveofourown.org/series/2145312
Comments: 10
Kudos: 54





	Invariance

**Author's Note:**

> Sequel to The Uncertainty Principle, though you don’t necessarily need to read that to follow along. 
> 
> It’s Fitz’s point of view, so buckle up, folks- here be swear words. Lots of them.

Without a doubt, it had been the strangest twenty-four hours of Fitz’s life. And for someone who had literally jumped through a fucking _rock_ and landed on another planet (not once, but _twice_ ) ...well, that was saying a lot.

A mere twenty-four hours ago, he had been happily minding his own fucking business from the comfort of his bunk at the Playground- recovering from the most mind-blowing orgasm of his life, securely cuddled up with the only woman he had ever loved, and finally believing that maybe there actually _was_ a place in the universe for him. 

And then, approximately seven minutes later at bullshit- o’clock, the universe had determined it was as good a time as any to tell him to go fuck himself. 

This time around, the cosmos had decided to use the reanimated corpse of Grant Ward and a brainwashed Daisy Johnson to _literally_ shake him out of a blissful, post-orgasmic haze by quaking the piss out of the base and dropping a decently-sized chunk of drywall on his head. 

(At the very least, he couldn’t deny that the universe was getting increasingly more creative with its metaphorical dick-punching, all things considered). 

On any other day, the events had that followed Daisy’s escape from the Playground would have felt like just another day at the fucking office. Flying to a foreign country on a moment’s notice, infiltrating a transhumanist black market with a pair of cybernetic eyes in a briefcase, and getting Force- choked by one of his best friends? Par for the S.H.I.E.L.D. course, as far as Fitz was concerned. 

But flying to a foreign country on a moment’s notice, infiltrating a transhumanist black market with a pair of cybernetic eyes in a briefcase, and getting Force-choked by one of his best friends while the voice of Jemma Simmons saying the phrase “I’m going to take your cock out now and suck you off” played on a continuous loop inside his head? Well, that was a variable strong enough to throw his entire ecological perception completely off its axis. 

And resisting the urge to chase said variable down the rabbit-hole in his brain and pull up the corresponding visuals had become increasingly more difficult as the day wore on, much to his irritation. After all, there was a mission to complete. A friend to save. An unstoppable enemy to, well, _stop._ Yesterday, those were all problems that would have received his undivided attention and laser-sharp focus. 

But today? Well, today Fitz was living in a whole new world. A world in which those imminent crises were suddenly forced to share brain space with the ongoing mental TED Talk he was giving his dick about priorities and professionalism. 

(A talk that sounded strikingly similar to the conversation he had initiated with Jemma prior to boarding the quinjet for Romania, except with _much_ saltier language and a completely disinterested and defiant audience).

By the time the dust had finally settled on their failed mission and Fitz had dragged his sorry arse back to the rendezvous point, he was utterly exhausted in every way possible. His body was bruised, his mind was fried, and the amount of energy he had expended trying to block the image of Jemma’s lips wrapped around his cock could have powered a small city for at least a week. 

Paradoxically, that exhaustion served him well once he was safely past the threshold of the hotel room door. He was simply too tired to overthink, running on pure instinct and adrenaline as he and Jemma crashed together, frantically ripping at each other’s clothes and falling onto the bed in a frantic tangle of lips and tongues and wandering hands.

Jemma clearly had the upper hand on him when it came to which one of them could strip the other the fastest. She somehow had him down to his boxers before he even got her blouse off (though he couldn’t say he was surprised – between the two of them, she had always been the more goal- oriented one). Eventually, he got her on her back and was able to press several hungry kisses between her lace-clad breasts ( _black_ lace, no less, sweet fucking _Jesus_ ) before shifting his focus to her leather leggings. 

“Tell me what you want,” she said breathlessly, propping herself up on her elbows to watch as he knelt at the end of the bed and worked her skintight trousers down her legs.

Fitz shot her a quizzical look. “Am I not being obvious enough?” he asked, arching his eyebrows with a smirk. He freed her legs from the leggings and made an exaggerated show of tossing them over his shoulder, causing her to giggle. He smiled as he leaned down to press a kiss to her ankle bone. “I want _you_ ,” he murmured, trailing his lips up the inside of her calf to her knee, running the tips of his fingers up the soft skin of her inner thigh. 

“No, I mean – _tell_ me,” Jemma said forcefully. Fitz glanced up, momentarily confused. She was gazing down at him with a look that he had never seen on her face before. Especially not any look she had ever given _him_ . Her eyes were so full of ferocity and anticipation and, well, _lust,_ that for a moment she was almost unrecognizable. Fitz swallowed hard, temporarily paralyzed and unsure how to proceed, when he caught a familiar sparkle in her eyes and a quirk of her lips, and there she was again. His Jemma. He raised a questioning eyebrow and she nodded slightly, her cheeks flushed. That’s all it took – one brief, wordless conversation - and he understood what she was asking for. 

“You want me to tell you… what I want to do to you?” he asked, his voice low and remarkably steady, given the current state of his nerves. Jemma nodded enthusiastically, catching her bottom lip between her teeth as she watched him intently. “In detail, please,” she said sweetly, polite and proper as ever, though her voice had taken on a roughened quality that again, was both familiar and remarkably unfamiliar. She shot him a wicked grin. “ _Explicit_ detail.”

Fitz blinked. _Holy shit_. 

He exhaled slowly and carefully – his gut told him that wheezing was probably a mood-killer – and crawled over her body on his hands and knees until his face was hovering inches above hers. “How explicit is _too_ explicit?” he asked breathlessly, his heart hammering in his chest. He wanted to make sure he _completely_ understood what she was asking for, because _boy,_ did he have explicit details of what he wanted to do to every last inch of her. Ten years worth of explicit details, to be exact.

He watched as her eyes dilated and her skin flushed pink. “Use _all_ the naughty words,” she whispered with a cheeky smile, and before his brain could even begin to process _that_ statement _,_ she surged her head off of the pillow, capturing his mouth with her lips and tongue. All he could do was groan helplessly against her mouth as he returned the kiss and tried his hardest not to collapse on top of her. He carefully lowered himself onto his forearms and stretched his body out until his pelvis was lined up perfectly with hers, and rolled his hips forward experimentally. 

She broke away from his lips with a gasp and a shudder, arching her back and pressing up against his cock. He could feel her legs shaking as she brought them up to bracket his hips, her blunt nails digging into his shoulder in a way that signaled that he would have some substantial marks on his skin come morning. He latched his mouth to the soft skin above her collarbone and rocked his hips again, harder this time, and could feel her labia parting around the ridge of his erection, her wet heat palpable on his cock despite the layers of fabric that still separated them. 

“Fitz – _please_ ,” she whispered hoarsely, gripping his shoulders even tighter. He tucked his face into the crook of her neck and paused, inhaling the scent of her skin and doing his best to work up the courage to give her what she wanted. 

It wasn’t that he was naive or inexperienced when it came to sex - he had a small collection of short- term relationships under his belt, and had also gone on a bit of a tear the year he turned 21 (apparently a common phenomenon in America. When in Rome, indeed). But the stakes had never seemed quite as high as they did at the present moment. The last thing he wanted to do was say the wrong thing and freak her out. Or not say _enough_ and frustrate her. 

While Fitz tried to steady himself, the conversation they had shared outside of Radcliffe’s lab suddenly popped into his head, and a smug, obnoxious voice that sounded strikingly like his own urged him to take his own advice and “stop thinking altogether”. After all, the woman of his dreams was nearly naked beneath him and begging him to talk dirty to her. What further endorsement was he looking for?

_Stop thinking. Just do._

_When in Rome._

“I want suck on your tits,” he growled against her throat, sliding his hand down to the lace of her bra cup and pulling it down to reveal one perfectly round, pink-tipped breast. He allowed himself a millisecond to stare – he figured that spending the better part of a decade of daydreaming about what was underneath her jumpers was enough to award him a split-second of stunned gawking – before leaning down and closing his lips around her nipple. Her hands immediately flew up to cradle his head and she whimpered softly as he began to tease her with his tongue, testing her level of sensitivity. Stray observations collected from years of sharing overly air-conditioned labs had conclusively informed him that she was _definitely_ sensitive to temperature changes, and he surmised that she would likely be just as responsive to tactile stimulation. 

The way her nipple immediately hardened beneath his tongue, coupled with the soft sighs and gasps that were falling from her lips, provided more than enough data to prove his initial hypothesis correct. He increased the pressure of his tongue, circling her areola before drawing the entire peak of her breast into his mouth and suckling hard as she threaded her fingers through his hair and arched encouragingly against his mouth. He moaned around the puckered skin against his tongue and blindly reached for her other breast, tugging at the fabric of her bra cup with more force than he had its predecessor. He rolled the other nipple between his fingers as he continued to lavish the breast in his mouth with his lips and tongue, occasionally grazing his teeth over the very tip and feeling a heady rush when her gentle gasps and sighs turned to outright moans. 

Fitz kissed his way over to her other breast and gave it the same treatment until Jemma was positively undulating beneath him. He pulled his mouth off her nipple with a pop and sat back on his haunches to take in the view below him. The sight of her sprawled out on her back, with her perfect tits pushed together and framed by the black lace of her bra, nipples hard and reddened by his mouth , was enough to knock the wind out of him. Her dark hair was fanned out beneath her, and she blinked up at him with a dazed expression, chest heaving, lips softly pouted. She looked adorable and beautiful and so fucking sexy, all at the same time. He couldn’t believe that she was really all his. 

“Fiiiitz,” Jemma whimpered, reaching up for his shoulders in an attempt to drag him back down to her chest. He caught her by the wrists and gently pulled her hands away, resisting the urge to laugh as she groaned dramatically, flopping back on the pillow and increasing her pout ten-fold. 

“I’m not done telling you what I want to do,” he murmured. He trailed his fingers down the soft, flat planes of her abdomen until he reached the waistband of her lacy black knickers. Her hips hitched upward in anticipation and she bit her lip again, watching him with wide, expectant eyes, and _fuck._ That lip-biting thing was going to be the death of him. 

Fitz exhaled a low breath. “I want to eat your pussy,” he said hoarsely, hoping he sounded more confident than felt. He heard her breath hitch, and felt her stomach muscles clenching slightly beneath his fingertips, which he took to be a good sign. He leaned down and pressed a soft kiss just above her navel, hoping she didn’t notice how much he was starting to tremble. “I want to know what you taste like when you come, with my tongue on your clit and…” He paused and took a quick breath, knowing that what he was about to say next was going to inform him _exactly_ where the line was on the dirty-talk front. “..and my fingers in your cunt,” he finished in a rush, trailing his lips down her abdomen and keeping his head bent low so she didn’t see how red his face had become. 

Jemma whimpered and arched up against his mouth in what seemed to be an encouraging manner, which meant the c-word was fair game. Thank Christ he had read the room correctly on _that_ one. 

He continued to kiss his way down her stomach, stopping where her pale, freckled skin met the black lace of her knickers and started to slide her panties down her hips, looking up and watching her closely for any sign that she wanted him to stop. Even though she had made it pretty clear what she wanted from him, he still lacked the confidence to be 100% sure. Maybe over time that confidence would come, but for now he still was having a hard time wrapping his brain around the idea that she wanted _him_ the same way he had always wanted her. Which at the moment was naked. Very naked. 

The way she eagerly lifted her ass off the bed to assist in the pants-removing process quickly shook any lingering doubts from his mind. As did the sight of the soaking wet fabric clinging to her pussy as he peeled the underwear down past her knees. He shuffled to the side as she pulled one leg up, shortening the distance the black lace had to travel until the fabric was no longer constraining her legs together. She immediately let her knees fall open, spreading herself wide open for him. 

Fitz settled on his stomach between the cradle of her thighs, scooting forward until his face was inches from her soaking core. “Jem – god. You’re so fucking wet,” he groaned, lightly tracing the lips of her pussy with the tip of his finger, committing the sight of her glistening pink folds and swollen clitoris to memory as he circled the rim of her entrance, watching with more than a fair amount of fascination as her vaginal muscles contracted at his slight touch. He adjusted his position to give him full use of both hands, using his thumbs to spread her labia open and fully expose her engorged clit. He leaned forward and flicked the tip of his tongue over the hardened nub several times before settling in and running his tongue around it in slow, wet circles.

The sound she made in response– part moan, part gasp, part sob – was going to haunt him for the rest of his fucking life. He honestly had no idea how he was ever going to be able to function in society again, now that he was burdened with firsthand knowledge of what Jemma Simmons sounded like while she was having her cunt licked. 

Her hands quickly returned to the back of his head, holding him in place as she rolled her hips against his mouth, undulating her pelvis in time with the movements of his tongue. He couldn’t stop the moan that escaped from his lips, momentarily overwhelmed by the feel of her wet flesh dragging against his face. He ground down into the mattress involuntarily, quickly realizing that he would need to change position and shift his weight off of his cock to stop himself from coming right then and there. He gently closed his lips around her clit as he settled on his knees and hooked his arms around her thighs, drawing her legs over his shoulders and forcing her hips and ass off the mattress. 

Jemma gasped sharply and shuddered against his mouth at the sudden change in position, a sentiment he definitely agreed with - with her legs spread wide and draped across his back, he now had unlimited access to every inch of her pussy, and he wasted no time taking advantage of the new angle. He bent low to press a heated, open-mouthed kiss to the apex of her folds and began licking and sucking every bit of pink flesh he could get his lips and tongue on, spurred on by her increasingly frantic whimpers. When he reached the entrance of her cunt, he licked his way into her tight channel using the curled tip of his tongue, taking a moment to revel in her sweet, musky taste before licking a slow, wet path back up to her clit.

“OH - oh, Fitz - that’s- _yes_ ,” Jemma moaned, tightening her grip on his hair. He hummed as picked up his pace, wiggling the tip of his tongue in an up-and-down motion over her clit. “Feels so good, _fuck_ \- don’t stop.”

Hearing Jemma Simmons say the word _fuck_ was a bit of a confusing moment for his poor body. She rarely cursed, and when she did, it was usually born of anger and said in a tone that was frightening enough to strike fear in the hearts of even the bravest men. Fitz nearly froze on instinct but recovered quickly to double down on his efforts, his cock now impossibly hard and his heart thundering in his ears. Apparently he was going to have to train his brain to understand that Jemma swearing didn’t always mean he was about to get yelled at. 

(Conversely, making sure he didn’t get an erection every time Jemma got angry was probably going to become a full-time job in the near future.) 

The way her legs began to shake against his back told him it was time for him to make good on his earlier promise, and he slowly slid two fingers into her cunt as he flattened his tongue out and pressed it firmly against her clit. She cried out and rocked against his face with such force that it nearly knocked him off balance. He pressed his free hand against her lower abdomen to hold her in place and continued to lick at her while he stroked his fingers inside of her wet heat, searching for that perfect spot to bring her over the edge. 

Fitz knew he had found it when he dragged his fingertips against a particularly swollen bit of flesh and Jemma practically launched her upper body off the bed, curling toward his head until she was almost bent in half, her grip on his hair painful enough to make him grimace, but not painful enough to compel him to stop. He slid his hand up from her belly to her breast bone, gently pressing her back until she was flat against the mattress again, his lips and tongue maintaining steady pressure on her clit. When he began massaging her g- spot with the pads of his fingers, moving in tight circles against the slick wall of her cunt, she went strikingly silent in such an abrupt way that he knew it wouldn’t take much more before she broke. 

He sucked her clit into his mouth and curled his fingers upward in one synchronous act, and that was it. He felt her entire body shake apart beneath him, and the breath she had been holding exploded from her lips in a long, broken wail. Her pussy clenched and fluttered around his fingers and her clit pulsed beneath his tongue as a flood of wetness coated his hand and dripped down his wrist. The sound of her heaving sobs as she rode out her pleasure against his face and fingers was overpowering, and he quickly reached down with his free hand to squeeze the base of his cock through the fabric of his pants, barely in time to stop himself from exploding all over the bedding. He carefully licked and stroked until her breathing began to slow and the tremors in her body gave way to gentle shivers. 

Jemma heaved a long, quiet sigh and finally went limp, her legs sliding off his shoulders and landing on either side of him with a graceless thump. He placed one last gentle kiss to her clit and carefully withdrew his fingers, wiping them on the bedspread before crawling his way up her body again, stopping to nip at the underside of her breast with his teeth before finally settling on top of her, his face even with hers. 

“Jem,” he whispered hoarsely. She blinked her eyes open and gazed up at him with a look that would best be described as “stunned adoration”. Her hands came up to cradle his face and pull him down for a messy kiss, and he felt himself start to shake with desperation as he surged forward, tangling his tongue with hers and pressing his still-clothed erection against her drenched center. 

Jemma pulled away from his mouth and moved her hands to the waist of his boxers. “Off,” she breathed, pushing the fabric down his hips. 

He needed no further encouragement, flipping to the side and landing on his back with a bounce. He lifted his hips off the mattress and pushed his boxers down and off in record time before rolling back over her body. He pressed his chest to hers, pinning her beneath his full weight as the head of his prick slid through her folds. 

Fitz shuddered at the sensation of her wetness coating his cock. “Jemma,” he panted, pressing his forehead to hers and using his very last reserves of strength to refrain from rutting against her. He met her gaze, silently begging for permission, trembling as she drew her arms around his back and pressed her palms against his shoulder blades. 

“Tell me, Fitz,” Jemma said breathlessly, lightly scratching her nails down his back. He shivered violently, at both the sensation of her hands on his skin and the implication of the words that fell from her lips, and felt the last vestiges of his restraint begin to slip away. She tilted her hips up and wrapped her legs around the small of his back, bringing him closer to exactly where he wanted to be. “Tell me what you want,” she moaned softly against the shell of his ear, arching her hips off the bed and wiggling her soaking wet pussy against his shaft. 

She was obviously trying to kill him. 

Fitz had never moved so fast in his life, reaching down with one hand and positioning himself at her entrance. “I want you to beg for my cock,” he gasped out, pressing the blunt head of his erection against her cunt and sliding just the very tip into her tight channel, using the fist around his shaft to physically stop from himself pushing in any further. 

Her eyes widened in surprise, and _bloody fucking hell_ , she wasn’t the only one who was caught off guard by that statement. Up until that moment, he wasn’t sure if he was even going to be able to form actual _words,_ let alone say…well… _that._ Fitz had never asked anyone to beg for _anything_ before in his entire life. Why he chose _this particular_ moment to start making demands on behalf of his cock was well beyond his level of comprehension, particularly since he had spent the last few minutes fighting to get to this point before blowing his load. 

Jemma closed her eyes and moaned. “Fitz- oh god – please,” she gasped, scrambling her hands down his back and grabbing his ass, urging him to push all the way in. He gritted his teeth and locked the elbow of the arm that was holding him up as he tightened the grip on his shaft, his knuckles once again preventing him from sliding all the way into her. 

“Beg for it, Jemma,” he growled, his voice practically unrecognizable to his own ears. She moaned again and stared up at him, her pleading eyes reflecting his own desperation. The head of his dick was absolutely throbbing where it sat against her wet heat, and he couldn’t help but wonder if maybe he was a bit of a masochist. 

“ _Say_ it,” he hissed, allowing himself to slide forward an inch, crown of his erection now fully encircled by her cunt. He closed his eyes and swore under his breath, his arm beginning to shake with the effort of keeping himself from fucking her into the mattress. 

Yup. _Definitely_ a masochist. 

“Give it to me, Fitz- oh fuck – _please_ ,” Jemma finally sobbed, finding her voice. She writhed beneath him, squeezing her legs around him so tightly he nearly lost his breath.“Give me your cock, fill me up, _fuck_ – I need it, _please Fitz_ , I-I can’t –“ 

He cut her off, crashing his mouth to hers as he finally gave in, releasing the death grip he had on his prick and thrusting all the way into her soaking heat. His groan was muffled by her lips and tongue, and he broke away to catch his breath, briefly dropping his forehead to her collarbone as he adjusted to the overpowering sensation of her cunt wrapped tightly around his cock. 

Jemma was already rocking her hips, trying to encourage him to move. “Fitz, god – I-I need –fuck me, _please,_ ” she pleaded, her voice becoming louder and more desperate-sounding by the second. He couldn’t hold back any longer, and began rolling his hips down to meet hers.

“You like this, Jem?” he asked roughly, pulling up to watch her face as he thrusted. “D’you like my hard cock in your tight little cunt? Like getting fucked like this? You feel so good, so fucking wet. Wanna make you come again, all over my cock, just like this.”

Jesus _Christ_. And to think that at the start he had been reluctant to talk dirty to her. Now all of a sudden he couldn’t seem to shut the fuck up. 

“Yes, oh- fuck – _harder_ Fitz, _fuck,_ your cock feels so good,” Jemma gasped out, lifting her hips clean off the bed and allowing him to thrust even deeper into her channel, and Fitz practically bit through his lower lip trying to contain the groan that erupted from his throat. 

“Jem- I’m not going to last much longer,” he panted and quickly switched tactics, staying deep inside of her as he began to grind his hips in slow circles, his pubic bone pressed flush against her clit. She gasped and shuddered beneath him, unwrapping her legs from his waist and planting her feet on the mattress for leverage as she arched her hips as high as she could manage. 

“I want to come with you,” she whimpered. “I-I’m so close, oh fuck, Fitz, I need…” her words trailed off into a high-pitch whine as she undulated her pelvis against his, her movements becoming jerky and less coordinated.

“ _Fuck,_ Jemma- I want you to come, want to feel your pussy milk my cock,” he gasped. He leaned back on his knees and grabbed her by the hips, coaxing her forward until her ass was resting on his thighs. “Tell me what you need, baby girl,” he demanded hoarsely as he began to thrust again, using the hands on her hips to push and pull her along his prick. 

Jemma gasped loudly, sliding her hands up her torso and grabbing her tits. “Play with my clit,” she moaned, rolling her nipples between her fingers and rocking her hips in time with his thrusts. He wasted no time, snaking one hand between her legs and resting it atop the soft curls at the apex of her sex. He gently pressed his thumb to her clit and was temporarily hypnotized by the sight of his cock sliding in and out of her pussy, his shaft glistening with her juices and her slick pink folds stretched around his girth. 

The pitch and volume of her desperate moans quickly snapped him out of his filthy reverie, and he got to work, lightly working her clit in small circles with his thumb and increasing the pace of his thrusts. He watched hungrily as she played with her bouncing tits, her eyes screwed shut and her beautiful features contorted into a mask of pleasure. Her head was arched back against the pillow, and her mouth hung open slightly as she gasped for air and _fuck_ – he wasn’t going to make it – 

He was seconds away from his own impending orgasm when his brain decided to suddenly fire back up, if only for a moment, to supply him with an interesting detail he had noticed when she had orgasmed in his lap back at the Playground (which at this point seemed like a literal lifetime ago). It was an aspect he hadn’t planned on delving into this soon in their sexual relationship, but well…desperate times called for desperate measures. 

It was time to let Jemma Simmons know what a good girl she was. 

“So fucking beautiful like this, Jemma,” he grounded out, his thumb sliding easily over her clit as he shifted the angle of his thrusts just enough to help him drive into her more deeply.“Tha’s my girl-so good at taking my cock, s’ gorgeous, Jem.” The wet sounds of their coupling echoing throughout the room, mixed with his ragged breathing and her gasping sobs, was just on the cusp of being too much to bear. His felt his lower belly begin to tighten, and he gritted his teeth, aiming to hold out _just_ a little bit more. 

“Wanna fill you up, Jemma- give you my come ‘til you’re burstin’, _fuck_ you’re so perfect, such a good, _good_ girl, Jem –“ he choked out, pressing his thumb firmly against her clit. He watched with hooded eyes as she arched sharply off the bed and came with a hoarse scream, her cunt clenching and pulsating around him with such force that he had no other option but to finally let go. He gasped and surged his hips forward, sheathing himself as deeply as he could just as his cock swelled and his orgasm exploded through his core. 

“Oh god, _fuck_ – shit, _Jemma-_ oh _fuck_ ,” he gasped as jet after jet of come pulsed from his cock, seemingly with no end in sight as wave upon wave of pleasure crashed over him. He felt like he was drowning, in the best possible way, his breath seizing in his chest as he continued to unload his (apparently) endless supply of ejaculate into her throbbing cunt. 

“Fitz, oh- oh, I can feel it- I feel it inside of me,” Jemma whimpered, her muscles clenching and releasing around his prick. “I – I think I- oh _my_ GOD –“ 

Her voice broke off and Fitz watched, slack-jawed, as her whole body stiffened and she spiraled into what appeared to be another orgasm. He lunged forward and captured her mouth with his, swallowing her gasps and moans as he rode out the rest of his completion with his chest pressed firmly to hers, his hands in her hair and his tongue claiming her mouth. 

He ultimately had to break away from her lips in order to catch some air, and took several deep, steadying breaths before he collapsed against her body, pressing his face against her neck and feeling his muscles tremble as small aftershocks rocketed up from where his cock still buried deep inside of her. She circled her arms around his back and held on to him tightly as her vaginal muscles continued to contract and relax around his softening erection. Eventually, he felt her body relax and melt back against the bed linens as she came back down from her high. 

Fitz slowly returned to his senses, and realizing that he was probably crushing her with his weight, gently rolled off of her, his cock slipping out of her channel in a flood of wetness that made both of them hiss. 

“Sorry,” he said with a grimace, settling a hand on her hip and gently coaxing her on her side until she was facing him. She blinked her eyes open and gazed at him, a soft smile on her lips. 

“I don’t think you have anything to apologize for,” she said, brushing the tip of her nose against his before leaning forward and kissing him softly, reaching up to card her fingers through his hair. “On the contrary, “ she continued, pressing gentle pecks to his jaw, “I should be thanking you. That was -”

“Bloody amazing,” he groaned softly, closing his eyes as she continued to place soft kisses to his face, the gentle sensation of her lips on his skin filling him with a different type of warmth, one that was at once completely familiar and strikingly new. 

“I was going to say _brilliant_ , but yes. Bloody amazing, indeed,” she replied with a smile in her voice. “I think that might have been a record for me. Three times. _Very_ impressive, Dr. Fitz.”

Fitz gently stroked his fingers along the crest of her hip bone. “I can’t take all the credit,” he murmured. “You’re an extremely inspiring test subject.”

He felt her shiver beneath his fingertips, and she scooted closer to him until her breasts were pressed flush to his chest. “It certainly didn’t take you long to figure out which buttons to push, particularly that last one,” she whispered, drawing him in for a slow, lingering kiss.

“C’mon Simmons, you’re a biologist, you know better than that. It’s called the clitoris,” he replied with a smirk. She huffed a laugh against his lips and reached down to give him a gentle swat on his ass. 

“That’s not what I meant,” she giggled, wiggling against him playfully. “I meant the, um, verbal button.”

“I know what you meant,” he said, cracking his eyes open and meeting her gaze. “And it wasn’t that hard to figure out. You like being good, and you’ve always liked to be praised.” He leaned in and kissed her slowly, sliding his hand down from her hip to cup her ass. “I like that you’re a good girl,” he murmured, parting his lips and sliding his tongue gently into her mouth. 

Jemma hummed and pressed closer, stroking her nails lightly down his spine as she languidly returned the kiss. After a few moments she broke away, moving her hand to his chest and pushing gently until they were face to face again. “I like that you like that,” she said with a smile. She met his eyes, and her gaze suddenly took on a mischievous glint. “But sometimes…” she whispered, leaning in to trail a series of kisses from his collarbone up to behind his ear. “...I _do_ enjoy being a naughty girl. On occasion.”

No amount of mental stamina in the world could have stopped his dick from twitching at _that._ “Jemma,” he groaned, shifting his hips away from her before his cock could get any bright ideas. “That’s just unfair.”

Jemma laughed softly. “Down boy,” she teased. She glanced down at his cock. “Both of you.”

“Leave him out of this. He can’t think for himself,” Fitz grumbled, closing his eyes again and suddenly feeling like he could sleep for days on end. They stayed like that for several minutes, wrapped up in each other's arms, and he could feel himself starting to drift off. 

After some time, he felt Jemma slide her hand up to his shoulder to gently shake him. “Fitz, don’t fall asleep,” she said quietly. “We can’t stay here forever.”

“The hell we can’t,” Fitz muttered, even though he knew she was right. Mack was waiting for them on the quinjet, as well as a whole new set of impossible problems they needed to solve yesterday. That didn’t mean he had to be happy about it. He snuggled closer to her and pouted. “I won’t go. You can’t make me,” he mumbled petulantly. He felt her chuckle softly as she began gently running her fingers over his face.

“We should get dressed in case Mack walks in,” she murmured, tracing her fingertip up and down the bridge of his nose. “Poor man has had a rough enough day as it is. We don’t need to scar him any further.”

“Mack’ll be fine,” he mumbled sleepily, eyes still closed. “He spent most of his evening staring at robot tits via backscatter imaging. Natural nudity probably wouldn’t even phase him at this point.”

Jemma giggled. “It’s too bad neither you or I have any musical abilities,” she said. “Because Robot Tits would be an excellent band name.”

“I think it was the title of one of those lost _Doctor Who_ episodes, actually,” Fitz replied with a grin, and Jemma burst out laughing. He opened his eyes and felt his heart swell as he watched her dissolve into giggles, her smile dazzling and eyes sparkling in a way that he knew was only for him. Of all the fantastic noises he had heard her make over the course of the evening (and there _had_ been some spectacular ones, no doubt), nothing could ever compare to her laughter. 

It was his favorite sound in the world, it had been since he was 16 years old, and he wanted to hear it every single day for the rest of his life. 

“I might have been wrong earlier,” Fitz said, brushing a lock of hair away from her face. “What I said in the lounge, about the singularity and exponential change and all of that. Well, not _completely_ wrong, but I forgot a critical detail.”

Jemma raised an eyebrow. “Oh, you did?” she questioned. “And what’s that?”

“I didn’t consider the invariant.”

“The invariant? You mean the thing that -“

“-that doesn’t change, yeah,” he continued, finishing her sentence. “Like the law of gravity- it doesn’t matter where two objects are in space and time, the force between them-“

“-will always be measured the same way, regardless of any transformation that has already taken place or has yet to occur,” she finished with a smile. 

“Right,” he said. “Everything changes, and is constantly changing, but our connection won’t. That link we have, that we’ve _always_ had - it’s immutable, no matter what the universe chooses to throw at us. That’s how I know we’re going to be okay.” He reached out and stroked her cheekbone with his thumb, gazing into her bright eyes and nearly overcome by the love he saw behind them.

She nuzzled sweetly against his hand. “So... our love is officially a law of physics now?” she replied, beaming. 

Fitz shrugged. “I don’t make the rules, I just follow them,” he said with a grin. 

Jemma giggled. “What a good boy,” she murmured, pulling him down for one more kiss. 

  
  
  


**Author's Note:**

> While I love Fitz's speech about the singularity in transhumanism, I always thought it was maybe not the most romantic sentiment, seeing as the singularity usually refers to the theoretical point in which artificial intelligence overtakes human intelligence (though, given the events of Season 4, it was stunningly prescient of him). I don't know about you, but if someone indicated that sleeping with me would eventually lead to Judgment Day, I'm not sure I'd hit it, no matter how cute he was. 
> 
> But I digress. 
> 
> This fic was my take on what I think he was trying to say, or would have said had the Cybernetic-Titted lady not interrupted them. In general terms, an invariant is a factor that doesn't change, and in psychology specifically, an invariance is something a person can recognize from any vantage point, regardless of the circumstances. 
> 
> Thank you for reading. Follow me on tumblr if late-night reblogs with angry/horny tags are your thing: https://pictures-to-prove-it.tumblr.com/


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